If you're shooting video with the Panasonic GH3, I highly advise you take a look at the Fhugen GH3 Video Cage. It's compact enough that you can leave your camera in there the entire time, and will give you more mounting points for adding on those necessary accessories. One question that comes up often is 'How do you add rails to the Fhugen Cage?'.
Although there isn't a dedicated 15mm rod adapter for the cage, the design is straight forward much like the tripod mount under your camera. You can mount it to a variety of baseplates that support 15mm rails (and yes it will be optically centered).
In the example above i'm using the PNCGear MP-2 dual rod baseplate (found here). There are height adjustments on the MP-2 if you need to make your rails slightly higher or lower. The baseplate can be used in any direction, but here I have the logo on the side of the LCD screen. Under the baseplate is enough tripod mounts to add your quick release plate of choice for tripod mounting.
 Fhugen Honu Video Cage for Panasonic GH3 Cameras |
 MP-2 Dual 15mm Rail Baseplate |
 (2) 15mm Rails for Baseplate |
